A multiple-input multiple-output (MIMO) technology based on a multiple-antenna system is one of key technologies for 3G and 4G wireless air interfaces. Without increasing usage of time-frequency resources, the MIMO technology can double spectrum efficiency by effectively using degrees of freedom in space domain. To effectively use the degrees of freedom in space domain, both a signal transmit end and a signal receive end need to obtain channel information.
Generally, the receive end may calculate channel information by receiving and demodulating a known training sequence symbol, but the transmit end can obtain channel information only by using a channel information feedback mechanism. As wireless broadband applications such as mobile multimedia continuously pose new challenges on bandwidth of a communications system, using a massive MIMO technology based on a massive antenna system as one of key technologies for a future 5G wireless air interface has become a consensus in the industry. As in the foregoing MIMO technology, to effectively use massive degrees of freedom in space domain and significantly enhance spectrum efficiency, both the receive end and the transmit end are required to know channel information. Channel information dimensions corresponding to the massive antenna increase significantly. Therefore, design of a channel information feedback method and mechanism is especially important.
The prior art provides a channel information feedback method. A base station (BS) side obtains downlink channel state information, and uses a channel state information feedback solution based on a codebook. The codebook is a predetermined M×N matrix C, where each column vector is referred to as a codeword, indicated by C=[C1, C2, . . . , Ci, . . . , CN]. A quantity of elements included in each codeword is referred to as a dimension of the codeword, and corresponds to a dimension of measured channel information. The channel state information feedback solution based on the codebook is as follows: User equipment (UE) selects, according to a predefined rule, a specific codeword Ci for channel state information (M×1 vector) to be fed back, and then transmits a sequence number i of the codeword in the codebook to the BS side by using an uplink channel. The BS selects, from the codeword book C according to the sequence number i, the codeword Ci as an estimated input value of downlink channel information.
A disadvantage of the prior art is that downlink channel estimation uniquely corresponds to a single codeword in the codebook in the prior art. A single codeword is used to represent channel estimation. Therefore, precision of channel estimation severely depends on a spatial resolution of a specific codebook. For the conventional MIMO system, because there are few BS antenna array elements, and a dimension of a codeword in a codebook in the system is relatively low, a spatial resolution of a codeword can be enhanced easily by increasing a quantity of codewords. However, with significant increase of antenna array elements configured for a massive MIMO BS, enhancing a spatial resolution by increasing a quantity of high-dimensional codewords becomes extremely difficult, both in a theoretical method and an engineering implementation.